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  3. Everyone has suffered from headaches, but【C1】______recently medical researchers were not certain what caused them. Blew research

Everyone has suffered from headaches, but【C1】______recently medical researchers were not certain what caused them. Blew research

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问题     Everyone has suffered from headaches, but【C1】______recently medical researchers were not certain what caused them. Blew research is giving us more【C2】______about two common types of headaches: tension headaches and migraine headaches. The most painful【C3】______are migraines, which【C4】______about eight to ten percent of the time and are【C5】______as a very sharp, throbbing pain. Most heada ches,【C6】______, are tension headaches. They are unpleasant, of course, but not as painful as the migraine【C7】______. Usually they are experienced as a(n)【C8】______ache on both sides of the head or in the back or forehead. These headaches are caused by the tightening of the muscles of the head and neck, which【C9】______causes the blood vessels to narrow, making it difficult for the brain to receive the oxygen(water, nutrition, blood) it needs. This is what causes the pain. Migraines,【C10】______, result from the blood vessels in the brain enlarging, causing swelling in the brain. This swelling results in terrible pain. The headache may last for a day or two and【C11】______the individual sick and weak. Migraines are apparently【C12】______, because several individuals in the same family usually have them. Doctors believe that the brains of these individuals【C13】______in unusual ways to small problems, like failing a test or eating unwisely.【C14】______there are warning【C15】______before a migraine occurs, such as spots appearing before the eyes or a sick feeling in the【C16】______. If the person takes medicine or caffeine as soon as he or she begins to feel the headache coming【C17】______, it can be【C18】______. Caffeine and the medicine, called ergot, cause the blood vessels to narrow. Once the headache【C19】______, sleep and a cool【C20】______on the head may help.
【C19】
选项 A、acted
B、started
C、has started
D、has acted
答案C
解析 此句意为“一旦疼痛发生”，用现在完成时较合适，另外，start要比act“行动”更符合句意，所以此处用has started。
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